Power Supply Arc Cut-off

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I've welded since 1992, and professionally now for about a year. I learned on "modern" machines, and so I'm unfamiliar with welding machines made before, say, the 1990's.I work in a shop that has large Airco brand power supplies for the Mig and Tig welders. I don't know for sure, but judging by the fonts of the words printed on the machines, and general age assessment, I'd guess that they were built in the early 1960's. One machine in particular intrigues me. It is the power supply for a Tig welder, and has, of course, a remote foot pedal. A toggle switch allows the foot switch to be active or not. The machine is "scratch start" only. My concern is this; when I come to the end of the weld, I can't terminate the arc by simply taking my foot off the pedal. I have to flick the electrode away, and thus take away the shielding gas when the molten puddle is still hot. This almost always leaves a semi-burned patch at the end of the bead, or a burned tack.I'm told by an old-timer at the shop that the machine is functioning correctly, and that THIS IS THE WAY THINGS ALWAYS WERE, back in the day.I guess I'm spoiled, because I own a Miller Syncrowave 180, with which I'm totally satisfied. It of course has arc start and post purge, so as to lessen fouled electrodes and burned beads.Is the Airco machine functioning properly, or should even "vintage" machines terminate the arc when the foot pedal is lifted?
Reply:Ahhhhh, you are looking for sage advice from one of the 'ancient ones' who frequent this site.  One of them will be along soon (it's their nappy time).
Reply:Is there another switch to change contactor control on to the remote pedal?  I have a 1986 Dialarc HF that has one toggle switch to change to remote amperage control and a seperate toggle switch to change to remote contactor control.Last edited by DesertRider33; 01-26-2008 at 05:13 PM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Don't whip it away just pull it out of the puddle slowly while easing off the pedal, hopefully you get used to it.
Reply:Originally Posted by DesertRider33Is there another switch to change contactor control on to the remote pedal?
Reply:Originally Posted by 65535Don't whip it away just pull it out of the puddle slowly while easing off the pedal, hopefully you get used to it.
Reply:I used an old machine like that out of the 60s and had the same problem.  I finally figured out why it had a switch on the torch AND a foot pedal.  I was doing the same thing, pulling the torch away at the end of the weld.  If I just took my foot off the pedal I had no post flow.  Tungsten turned black instantly.  Pulling away worked OK  for me.I learned on an old machine, then I got an inverter and learned again.  Its much easier with these newfangeled machines.  Great welds can be made with the old ones too.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Contactor is just a switch that turns the weld output power on and off.  The foot pedal normally operates just like you think it should-  no current when the foot pedal is up.  There are two components the foot pedal is operating.  One is a resistance circuit that varies the amperage within a set range from low to high, the base current level of which is controlled by the amperage setting on the machine (rheostat usually) and the other is an on-off switch that controls the contactor inside the machine.It sounds like the machine you're using is made for stick welding and has been adapted for TIG use.   No contactor is used in stick welding, the electrode is always hot, but a remote amperage control is sometimes used when welding far away from the machine.I have not tried to TIG weld with a torch that's always electrically hot, so I have no help to offer for that situation.I'm guessing the gas valve must be on the torch on your machine?Last edited by DesertRider33; 01-26-2008 at 06:16 PM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by DesertRider33I'm guessing the gas valve must be on the torch on your machine?
Reply:Now that's an interesting set up... Not one I would have ever thought of.  I think I'd look into moving the switch, either onto the torch or controlled by the foot pedal.  Sounds like there are some 'creative' people working in your shop....MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op